The invention relates to digital image processing, and, more particularly, to a method and apparatus for processing real-time raw image data and displaying the processed pixel signals in a real-time manner with programmability and high quality.
In a conventional digital signal processing system such as a digital still camera, an image sensor within an image-gathering means, such as a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor having a color filter array that provides a spatially color-sampled image, is exposed to image light and the resultant analog image information is converted by an analog-to-digital converter (ADC) to digital image signals. The digital image signals are then transferred to a memory such as a synchronous DRAM (SDRAM) or DRAM for temporary storage. Some digital still cameras have color liquid crystal displays (LCD), which are also spatially color-sampled devices. As the user typically intends to preview the image prior to capturing it for storage, the digital image signals are transferred to a preview mode apparatus (hereinafter referred to as a preview engine) for previewing the picture frame prior to capturing the image.
Usually, as the user would like to immediately preview the image of the picture on the LCD as the camera is moved over the subject, real-time operation in the preview mode is practically essential. That is to say, for typical digital still cameras, the processing used in the preview mode must be done rapidly, such as 60 images per second to avoid any perceivable display delay. The term xe2x80x9creal-timexe2x80x9d is applied herein to operations achieved without substantial perceivable display delay.
Despite the fact that the image quality of the displayed image is limited by the resolution and color gamut of the LCD screen of the LCD display, it is desirable for the preview image to reflect the qualities of the final image produced by the camera. To accomplish this, the preview engine would preferably include the functions used to produce the final image, functions such as white balance, auto exposure, auto focus, gain control, gamma correction, and color space conversion. The enhanced preview image would also, of course, preferably be accomplished without added complexity or cost. Therefore, there is a need in the industry for a method and apparatus capable of upgrading the quality of the images previewed on the LCD display and to satisfy the desire for real-time operation in the preview mode by less complex and more cost-effective configurations.
In one embodiment of the invention, a method for previewing an image in a camera prior to output is disclosed. The method includes steps of gathering image data, storing the image data, calculating display parameters using the stored image data, storing the display parameters in a look-up table; and applying the display parameters in the look-up table to at least a portion of the image data to produce preview image data. The display parameters can be quickly calculated using a digital signal processor to achieve real-time image previewing. The parameters used in an embodiment camera are white balance, gain control, gamma correction, and color space conversion. Once calculated using a preview algorithm run on a digital signal processor, these parameters can be combined in one or more look-up tables that can be updated by the digital signal processor as imaging conditions demand.
In another embodiment of the invention, a method for previewing an image in a digital camera prior to output is disclosed. The method includes the steps of gathering image data, digitizing the image data, storing the digitized image data, sampling a portion of the digitized image data, calculating white balance adjustment and gain control parameters using the stored digitized image data, and storing the white balance adjustment and gain control parameters in a look-up table; and applying the white balance adjustment and gain control parameters in the look-up table to the portion of the digitized image data to produce preview image data.
In still another embodiment of the invention, a digital camera is disclosed. The digital camera includes an image-gathering device, a preview engine coupled to the image-gathering device, wherein the preview engine includes a look-up table, a display coupled to the preview engine, a storage device coupled to the image-gathering device; and a processor coupled to the look-up table and to the storage device.
An advantage of the invention is that it enables real-time processing of desirable imaging features such as white balance, gain control, gamma correction, and color interpolation.